Human beings, especially elderly persons, frequently tend to lose vision due to a gradually increasing clouding of the natural lens of the eye, which results from the development of a degree of opacity or clouding of the fibers (the cortex) surrounding the inert nucleus of the natural lens within the capsular bag housing the same, i.e., between the anterior and posterior capsules of the bag (the anterior capsule is the wall of the bag which is closer to the cornea, and the posterior capsule is the wall of the bag which is closer to the retina). The condition where this opacity spreads into the center of the lens in the region behind the pupil so as to impair vision, is designated cataract. When the opacity has progressed sufficiently to cause the loss of useful functional vision, the cataract is said to be mature, and the only currently available treatment for that condition is the removal of the cataract by extraction of the natural lens from the eye and the replacement of the natural lens by an artificial lens.
Merely by way of definition, a cataract removal, if it entails an extraction of the entire lens (including the nucleus, the cortex (the fibers) and the enveloping capsular bag) as a unit, is identified as an intracapsular cataract extraction (ICCE). On the other hand, a cataract removal which entails an extraction of only the lens nucleus and the cortex from the endogenous capsular bag through an opening formed by cutting away the mid-region of the anterior capsule and leaves in place only that residual part of the capsular bag which consists of the posterior capsule and the remaining annular anterior capsular flap, is identified as an extracapsular cataract extraction (ECCE).
The usual follow-up to an ECCE is the implantation of an artificial intraocular lens (IOL) into the posterior chamber of the eye (the anterior chamber is the space between the cornea and the iris while the posterior chamber is the space between the iris and the capsular bag), with the haptics of the IOL then being seated either in the ciliary sulcus outside and just anteriorly of the residual capsular bag and posteriorly of the iris, so that the entire residual capsular bag isolates the IOL from the vitreous humor, or physically within the residual capsular bag at the equatorial region thereof where the anterior capsular flap adjoins the posterior capsule, so that only the posterior capsule of the residual capsular bag isolates the IOL from the vitreous humor. There are, of course, many types of IOLs, designed for implantation into either the anterior chamber or the posterior chamber of the eye, which over the years have been developed and available to eye surgeons for use in cataract surgery (representative ones are shown in Kelman U.S. Pat. Nos. 4,092,743, 4,174,543 and 4,608,049; Hoffer U.S. Pat. No. 4,244,060; Poler U.S. Pat. No. 4,402,579; Siepser U.S. Pat. No. 4,556,998; Ginsberg et al. U.S. Pat. No. 4,562,600; Mazzocco U.S. Pat. No. 4,573,998; Sayano et al. U.S. Pat. No. 4,681,585; Smith U.S. Pat. No. 4,704,123; Anis U.S. Pat. No. 4,795,460; Goldberg et al. U.S. Pat. No. 4,806,382; and Choyce U.K. Pat. No. 2,081,469), but since the designs and other features of most of these lenses are by and large not germane to the present invention, they will not be further discussed in detail herein.
While posterior chamber IOLs have proven to be of great benefit to persons who have undergone an ECCE, some post-operative complications do occasionally arise in connection therewith. As mentioned in my prior application Ser. No. 08/060,636, one such complication is a post-implantation clouding of the posterior capsule which is a consequence of the fact that some epithelial cells are almost invariably left in the equatorial region of the capsular bag and not removed therefrom during the irrigation and aspiration phase after the surgeon has extracted the cataract. These cells have a tendency to migrate over the anterior surface of the posterior capsule toward the center or optic region thereof and, upon accumulating there, lead to capsular fibrosis and the formation of Elschnig's pearls, which in turn causes opacification of the posterior capsule and ultimately impairs vision in the same manner as the original cataract did, namely, by blocking the passage of light through the capsule to the retina. To remedy this situation, a further surgical procedure then becomes necessary, which may involve scraping and cleaning the accumulated fibers from the anterior surface of the posterior capsule behind the implanted IOL and possibly even a cutting out of the opacified region of the posterior capsule by means of a laser capsulotomy (which of late has substantially supplanted knife discission as the standard operating procedure). In any event, the possibility that the patient may be traumatized or even develop retinal detachment by such a procedure, coming after the patient has already gone through two losses of vision and one or two surgical procedures (the ECCE and the IOL implantation), is a prospect to be avoided.
The problems of capsular fibrosis and formation of Elschnig's pearls and of the resultant opacification of the posterior capsule following an ECCE have been recognized in the technical and patent literature; see, for example, the discussions thereof in the aforementioned U.S. Pat. Nos. 4,244,060 (Hoffer) and 4,562,600 (Ginsberg et al.). However, neither the ridged Hoffer lens nor the flanged Ginsberg lens described in those patents has been successful in eliminating these problems, in essence for the reason that in each of these lens designs one or more recesses are formed in the ridge or flange which projects posteriorly from the lens optic and is in contact with the front or anterior surface of the posterior capsule once the IOL has been implanted. Hoffer taught that such recesses (which are designated by reference numeral 34 in U.S. Pat. No. 4,244,060) are useful because they facilitate performance of a knife discission of a clouded posterior capsule without necessitating a dislodgement of the IOL. Ginsberg et al. taught that such recesses (which are designated by reference numerals 34 and 36 in U.S. Pat. No. 4,562,600) are useful because they facilitate rotational positioning of the IOL during the initial implant surgery and also minimize the post-implantation occurrence of unwanted and disturbing light reflections into the visual field. However, such recesses constitute breaches or gaps in the ridge or flange element of the lens which actually permit that which the ridge or flange of the lens is nominally intended to inhibit, namely, the migration of the epithelial cells into the optic region of the posterior capsule from the equatorial region of the capsular bag. The Hoffer patent evidences no awareness of this problem at all and thus offers no solution therefor whatsoever, while the Ginsberg et al. patent, though recognizing the possibility of cell migration through the notch-like recesses in the lens flange, suggests only the substitution of somewhat smaller indentations or of round holes for the notches, which still leaves one or more gaps in the flange through which cells can migrate.
In both the Hoffer and Ginsberg lenses, furthermore, the ability of the epithelial cells to migrate from the equatorial region of the capsular bag toward the optic region of the posterior capsule is not inhibited in any way until the cells are practically in the optic region, i.e., when they reach the zone of contact of the ridge or flange with the posterior capsule. In the Hoffer lens, on the one hand, this is so because the hairs constituting the haptic structure of the lens, though they are received in the cleft or fornix of the capsular bag, do not exert mechanical pressure on the entire interior surface of the equatorial region of the bag. Thus, not only are there many locations where the cells are not killed by mechanical pressure, but the Hoffer lens actually relies of the presence of the cells and the resultant fibrosis to anchor the IOL in the capsular bag. At the same time, the haptic structure, by virtue of the very nature of the hairs, cannot ensure that the rim portions and the ridge of the lens are pressed against the posterior capsule to block the migration of the epithelial cells into, and hence the propagation of capsular fibrosis and the formation of Elschnig's pearls in, the optic region of the posterior capsule. In the Ginsberg lens, on the other hand, the haptics cannot even partially inhibit cell migration because they are seated in the ciliary sulcus outside the capsular bag, while at the same time they cannot fully ensure adequate pressure contact between the flange of the IOL and the posterior capsule, so that again capsular fibrosis and pearl formation are not inhibited. Moreover, by virtue of the fact that in both the Hoffer lens and the Ginsberg lens there is an open space defined between the posterior capsule and the rear or posterior face of the optic, pearl formation in the optic region of the posterior capsule is not only not inhibited but is actually promoted. Of course, even were the haptics of the Ginsberg lens seated in the capsular bag, they would still not serve to block cell migration over the entire circumferential extent of the equatorial region of the bag.
The invention disclosed in my aforesaid prior application provided a design for a posterior capsular opacification-inhibiting posterior chamber IOL adapted for in-the-bag implantation following an ECCE. The significant characteristic of that design was the presence, in surrounding relation to a central optic, of a pair of 360.degree. haptics constituted by two concentric endless rings of different diameters. When such an IOL is properly implanted, the outer ring, the plane of which is anteriorly offset relative to the plane of the inner ring, presses against the interior surface of the equatorial region of the capsular bag and constitutes a primary mechanical barrier to the migration of epithelial cells onto the posterior capsule and over the latter into the optic region thereof, while the inner ring presses against the anterior surface of the posterior capsule a short distance away from the equatorial region and constitutes a secondary mechanical barrier to the migration of epithelial cells into the optic region of the posterior capsule, thereby to inhibit capsular fibrosis and posterior capsular opacification. The offset between the rings also serves to maintain the posterior capsule flush and taut against the optic and thereby inhibits the formation of Elschnig's pearls on the posterior capsule.
IOLs embodying the dual 360.degree. haptic structure of my prior invention are unitary devices which are well suited for their intended purposes. It may happen, however, that an eye surgeon, in the exercise of his or her professional judgment, will wish to be able to implant into a patient's eye a standard type of IOL. Such an IOL, however, will not be provided with means enabling migration of epithelial cells from the equatorial region of the capsular bag toward the optic region of the posterior capsule and the formation of Elsching's pearls to be inhibited. Thus, the surgeon contemplating the use of such an IOL will inevitably be faced by the surgeon's dilemma, namely, having to secure the benefit of using a standard IOL at the cost of losing the above-described advantages and benefits of the dual 360.degree. haptic arrangement and at the risk of exposing the patient to post-operative posterior capsular opacification.